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What heats faster?

CloudHidden | Posted in Energy, Heating & Insulation on January 23, 2003 10:02am

A house has two equal RFH zones of 1200 ft, one for the left side, and one for the right side. 4 in slab. House is symmetrical, so no building or insulation differences. Ignore solar. Heat plant is sized smallish. If either zone operates alone, the heat plant can maintain a set point water temp of 115. If both operate concurrently, the water temperature stabilizes at about 100. If the goal is to heat the rooms to 70, which is a more efficient way to operate the heat:

* run both zones at the lower temp

* alternate running of the zones to take advantage of the higher temp and greater delta-T

Did I miss any assumption?

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Replies

  1. stonefever | Jan 24, 2003 04:03am | #1

    A wife going thru menopause.

    1. User avater
      CloudHidden | Jan 24, 2003 05:19am | #2

      On a 2 degree night, the extra btu's might be helpful!

  2. hammerinharry | Jan 24, 2003 06:24am | #3

    "If the goal is to heat the rooms to 70"

    I'd say run both zones at lower temp. If you alternate running zones you're always going to have cool areas and warm areas.

    Harry's Homeworks

    Rhode Island

    1. User avater
      CloudHidden | Jan 24, 2003 06:32am | #4

      >you're always going to have cool areas and warm areas.

      Don't forget that the thermal mass will mitigate some of that.

      1. hammerinharry | Jan 24, 2003 07:19am | #5

        You're right, thermal mass will mitigate some of it but I'll stick with both t'stats set on 70 and even heat throughout with the 70 degrees being the goal.Harry's Homeworks

        Rhode Island

  3. junkhound | Jan 24, 2003 08:08am | #6

    You're gonna make people have to think about how & why hot water freezes into ice cubes Faster than cold water again <G>

    Assuming the 'plant' is gs heat pump, obviously the COP is higher with 100 F water so that  is more efficient, thus run both (effectively bigger condensor as you already know)

    1. bearmon | Jan 24, 2003 09:05am | #7

      how & why hot water freezes into ice cubes Faster than cold water again

      Sorry, but it doesn't.  Water that has been heated, & then cooled to the same temp as the other water, will freeze faster, because some of the disolved gases will now be gone, but hot water will never freeze faster than cooler water. Bear

      1. junkhound | Jan 24, 2003 04:40pm | #8

        OK , forgot to add the detail that we are talking the same original mass of water -- or same volume; BTW, for same starting volume, the hot water freezes even faster.

    2. User avater
      BossHog | Jan 24, 2003 06:56pm | #9

      "You're gonna make people have to think about how & why hot water freezes into ice cubes Faster than cold water again "

      HEY! - Let's start a new thread about that in the tavern, so we can start another endless and pointless debate about something besides politics.You never really learn to swear until you learn to drive.

      1. NormKerr | Jan 24, 2003 08:35pm | #10

        I say run both constantly at a lower temp because the losses from a higher temp will more than offset any slight gains from the higher delta T.

        For radiant system you try to design to run at the lowest temp for that reason.

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